Some cities are at the forefront of finding and enforcing solutions to social and environmental problems; others remain stuck on the back benches. This dissertation examines the case of city climate action-strategic attempts to mitigate and adapt to climate change by local means---to understand the profound variation in cities' capacities to act. I bring together theories from organizational, political, and urban sociology to develop a framework of city action that shows the interplay of a place-based organizational ecosystem and a shared institutional environment. Comparative analyses of and expert interviews in cities in the United States and around the world show how public officials have shaped cities' responses to the changing climate. Three empirical chapters illuminate the global rise and stagnation of strategic commitments to tackling climate change, the political and institutional contexts of urban sustainability efforts in city administrations, and the public--private interactions in the origins and spread of green construction. Across these studies, civil society emerges as an anchor of urban innovation that leads by example, guides the actions of public administrations, and knits an emergent professional network of cities. This research contributes to sociological theory by inserting contemporaries Max Weber and Robert Park into a long due conversation that explains disparities in urban innovation. It also reveals durable differences in the organizational infrastructure of cities, which are shown to catalyze or curb city action by shaping civic and state capacities. Lastly, this research contributes to our understanding of organizational society in the urban age by its comparative study of meso-level mechanisms through which organizations influence their urban environment. In closing, I recall Charles Tilly's last book to caution against a bifurcation into isolated and networked cities.